Hot knives are typically used to simultaneously melt and sever sheet material such as organic polymeric material. A sharp edge is heated and brought into contact with the material, thereby melting the material along the line created by the sharp edge. However, two problems are known to exist with such hot knives.
One problem exists when the heated knife clings to the sheet material thereby causing stringing or re-welding of the severed material. U.S. Pat. No. 4,215,607 issued to William G. Hudson, et al on Aug. 5, 1980, discloses a hot knife including a wedged shape knife for severing the sheet material. The wedge shaped knife provides better severing of the sheet material, however, it has been found that since there is no refractory material, there is no cooling on the sheet material and thus the material tends to adhere to the blade and create stringing.
The U.S. Pat. No. 3,054,441 issued to Virgin E. Gex et al on Sept. 18, 1962, discloses a hot knife including a heated wire element positioned at an apex of a ceramic wedge. The wire is displaced through the sheet material thereby allowing the ceramic wedge to cool the severed material. Thus, stringing is prevented and a return path for the hot wire is created. However, it has been found that heating elements such as a wire, do not keep constant operating temperatures. The wire temperature has been found to constantly fluctuate between each severing process.